剑指offer 面试66题

面试66题：

题目：构建乘积数组

给定一个数组A[0,1,...,n-1],请构建一个数组B[0,1,...,n-1],其中B中的元素B[i]=A[0]*A[1]*...*A[i-1]*A[i+1]*...*A[n-1]。不能使用除法。

根据剑指offer思路

基本解法：

# -*- coding:utf-8 -*-
class Solution:
    def multiply(self, A):
        # write code here
        n=len(A)
        C=[1]*len(A)
        D=[1]*len(A)
        B=[1]*len(A)
        for i in range(1,n):
            C[i]=C[i-1]*A[i-1]
        for j in (range(0,n-1))[::-1]:
            D[j]=D[j+1]*A[j+1]

        for k in range(0,n):
            B[k]=C[k]*D[k]
        return B

优化代码如下：

# -*- coding:utf-8 -*-
class Solution:
    def multiply(self, A):
        # write code here
        B=[1]*len(A)
        for i in range(1,len(A)):
            B[i]=B[i-1]*A[i-1]

        tmp=1
        for j in range(len(A)-2,-1,-1):
            tmp *= A[j+1]
            B[j]*= tmp
        return B